The present invention relates generally to cooling of jet engine components, and more particularly to impingement cooling of such components. The phrase "jet engine" includes gas turbine, ramjet, and scramjet engines. Such jet engines may be used to power flight vehicles, and the gas turbine engine type of jet engine may also be used to power ships, tanks, electric power generators, pipe line pumping apparatus, etc. For purposes of illustration, the invention will be described with respect to impingement cooling of an aircraft gas turbine engine component using cooling air. However, it is understood that the invention is equally applicable to impingement cooling of other types of jet engines (such as scramjets) and/or to impingement cooling using other cooling fluids (such as liquid fuel, water, steam, and the like).
A gas turbine engine includes a core engine having a high pressure compressor to compress the air flow entering the core engine, a combustor in which a mixture of fuel and the compressed air is burned to generate a hot propulsive gas flow, and a high pressure turbine which is rotated by the propulsive gas flow and which is connected by a shaft to drive the high pressure compressor. Engine thrust comes from the core engine airflow after it flows through the high pressure compressor to the combustor and is expanded past the high pressure turbine and out the exhaust nozzle. A gas turbine engine, such as an aircraft turbofan jet engine, may include other components, such as a thrust producing fan, a low pressure compressor, and a low pressure turbine.
Certain components of gas turbine engines, such as combustor liners, turbine airfoils (i.e., blades and vanes) and shrouds, and exhaust nozzles, are subjected to hot combustion gases. Current engine designs require that such components be cooled to keep their temperatures within design limits. A known technique for cooling gas turbine engine components is impingement cooling of a component wall surface, such as impingement cooling of a back surface of a combustor liner whose front surface is exposed to hot combustion gases. In this technique, a plate is spaced apart from the impingement cooled surface (e.g., the liner) and contains impingement cooling holes through which pressurized impingement cooling air flows in a jet-like fashion, impinging generally perpendicularly against the surface to be cooled (i.e., the impingement cooled surface, such as the liner). The "spent" cooling air (i.e., the post-impingement cooling air) typically flows out of the cooling zone by flowing generally parallel to the plate in the region between the plate and the impingement cooled surface (e.g., the liner). As crossflow from the (generally parallel-flowing) spent cooling air against the (generally perpendicularly-flowing) impingement cooling air weakens the impingement flow and lessens its heat transferring capabilities, techniques are needed to improve the effectiveness of impingement cooling.